Evaluation of stability constants of 1 (3 bromo 4 hydroxy 5 methoxy benzylidene) thiosemicarbazide(TRM 1) with copper (II), cobalt (II) and nickel (II) complexes by pH metric method

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Der Pharma Chemica, 2013, 5(4):244-251

(http://derpharmachemica.com/archive.html)

ISSN 0975-413X

CODEN (USA): PCHHAX

Evaluation of stability constants of 1-(3-bromo-4-hydroxy-5-methoxy

benzylidene) thiosemicarbazide(TRM-1) with copper (II), cobalt (II) and

nickel (II) complexes by pH metric method

Rakesh M. Tada*, Pankaj B. Nariya, Naimish K. Chavda and Manish K. Shah

Department of chemistry, Saurashtra University, Rajkot

_____________________________________________________________________________________________

ABSTRACT

This study was taken out for determine the stability constants of the complexes of 1-(3-bromo-4-hydroxy-5-methoxybenzylidene) thiosemicarbazide (TRM-1) in Dioxane: Water ratio 60: 40 (V/V) mixture by pH-Meter. The proton-ligand and metal-ligand stability constants of Cu(II), Ni(II) and Co(II) metal ions with TRM-1 have been performed pH metric method at 0.1 M ionic strength at 30°C ± 0.2°C temperature. The Proton-ligand stability

constants

log

pK

₁H,

log

pK

₂H and

log

β

H is 10.66, 3.11 and 13.77 respectively and the Metal ligand stability constants is determine different Computational Methods.

Keywords: Proton-ligand stability constants and Metal ligand stability constants,

1-(3-bromo-4-hydroxy-5-methoxybenzylidene) thiosemicarbazide, pH metric

_____________________________________________________________________________________________

INTRODUCTION

Recently, the high stability of the complexes prepared with vic-dioxime ligands have been extensively used for various purposes including model compounds for vitamin B12 analytical and medicinal chemistry, pigments [1, 2]. Schnauzer has found that this kind of complexes exhibits semiconductor property [3]. An investigation4 has been done about spectrometric and potentiometric characterizations of these kinds of compounds and stability constants with divalent metal ions.

Stability constants of metals complexes have been determined by many different methods such as spectroscopy [4] and potentiometry [5]. It is well-known that the simplest electroanalytical technique for determination of stability constants is potentiometric titration system used for the glass electrode. SUPERQUAD [6], a powerful computer program, was used in the evaluation of data obtained from this technique. In the literature, the synthesis of vic-dioximes and their various derivatives have been a subject of study for a long period of time [7]. The determination of the metal – ligand stability constant requires the knowledge of reliable and accurate values of proton-ligand stability constants. Thus, proton-ligand and metal-ligand stability constants are correlated with each other.

MATERIALS AND METHODS

Chemicals and Reagents

All the chemicals used in the present study were Analar grade. The glassware’s used in the present experiment were borosil glass quality and standardized as per standard procedure.

Preparation of the sample solution

The solutions of reagents were prepared in double glass distilled water having 6.80-6.90 pH. The NaOH solution was prepared in double distilled water and fresh solution was used as a titrant for pH titrations. It is standardized with 0.05 M succinic acid. The 1.0 M NaNo3 solutions were prepared to maintain the 0.1 M ionic strength of the titration solutions by taking requisite amount of Sodium nitrate. The metal solutions were standardized by usual procedure [12].

Digital pH meter

pH of solutions to calculate the proton ligand stability constants and metal ligand stability constants were measured with a EQUIP-TRONICS instrument (Model EQ-614) equipped with a combined electrode and magnetic stirrer pH-meter (accuracy ± 0.005 units) with a combined glass electrode assembly of pH range 0 to 14. This instrument has been built in an internal electronic voltage supply with a temperature compensator covering the range from 0 to 100°C. The instrument was calibrated with buffer solution of known pH before starting the pH titrations. All the necessary precautions were taken for smooth working of electrode [13].

Calvin Bjerrum pH titration

The following sets of solutions were prepared for pH titration.

Set 1 : 0.8 mL 0.1 M HNO3 + 11.2 mL distilled water + 24.0 mL dioxane + 4.0 mL 1 M NaNO3.

Set 2 : 0.8 mL 0.1 M HNO3 + 11.2 mL distilled water + 22.0 mL dioxane + 2.0 mL 0.1 M ligand solution + 4.0 mL 1 M NaNO3.

Set 3 : 0.8 mL 0.1 M HNO3 + 10.8 mL distilled water + 22.0 mL dioxane + 2.0 mL 0.1 M ligand solution + 4.0 mL 1 M NaNO3 + 0.4 mL 0.1 M metal solution.

The total volume (V°) of the every set is 40 mL. The ligand solutions were prepared in Dioxane : Water ratio 60 : 40 (V/V).

Solutions mentioned above sets were allowed to stand at a 30°C ± 0.2°C temperature for few minutes then titrated against standard alkali solution (NaOH 0.5 N) under an inert atmosphere of nitrogen. The change in the pH of the solution with each addition of alkali was recorded are given in TABLE 3.

RESULTS AND DISCUSSION

The proton-ligand stability constant and metal-ligand stability constants(Log K) of TRM-1and their complexes with Cu(II), Ni(II) and Co(II) metal ions determined in 60% dioxane-water mixture at 30°C ± 0.2°C.

We have studied the proton ligand stability constants and metal ligand stability constants at 30° ± 0.2°C temperatures for synthesized ligands and metal complexes by the Calvin Bjerrum titration technique adopted by Irvin and Rossotti.

Table 1: Proton-ligand stability constants of the ligands at 30°°°°±±±± 0.2°°°°C

Ligand

pK

H

1

log

log

pK

2H

H

β

log

Table 2: Metal ligand stability constant of M(TRM - 1)2 at 30°°°°±±±± 0.2°°°°C

Chelates Stability Constant Computational Methods

a b c d

Cu(TRM-1)2

1

log K

8.62 8.63 8.60 8.64

2

log K

4.73 4.71 4.76 4.72

2

log

β

13.35 13.34 13.36 13.36

Ni(TRM-1)2

1

log K

9.02 8.98 8.99 8.96

2

log K

5.61 5.62 5.62 5.66

2

log

β

14.63 14.63 14.61 14.62

Co(TRM-1)2

1

log K

8.61 8.60 8.61 8.63

2

log K

5.35 5.36 5.37 5.36

2

log

β

13.95 13.96 13.98 13.99

(a)Interpolation at half

n

values , (b) Least square method, (c) Linear plot method , (d)Point wise calculation method

Calvin and Wilson have demonstrated that pH measurements made during titrations with alkali solution of ligand in the presence and absence of metal ion could be employed to calculate the formation functions

n

A

,

n

and pL and

stability constants can be computed. Irving and Rossotti [14], titrated following solutions against standard sodium hydroxide solution N° keeping total volume V° constant.

The formation functions

n

A

,

n

and pL can be computed from the following eqations:

o o o o CL 1 2 1 A

T

)

V

V

(

)

E

N

)(

V

V

(

Y

n

+

−

−

−

=

(1)

)

T

)(

n

)(

V

V

(

)

E

N

)(

V

V

(

n

CM A 1 2 3 o o o o

+

+

−

=

(2)

o o o o

V

V

V

T

n

T

H

K

K

H

K

pL

CM CL H H H 3 2 2 1 1 10

...

]

[

]

[

1

log

×

+

−

+

+

+

=

o o o o

V

V

V

T

n

T

B

anti

pL

CM CL n H n n n 3 0 10

)

log

(

1

log

×

+

−

⋅

Σ

=

=

β

(3) Where,

Y = number of dissociable protons

V1, V2 and V3 = volume of alkali employed bring the solution 1, 2 and 3 to same pH value T_CL° = total concentration of the ligand

TCM° = total concentration of metal ion

By the knowledge of

n

A

,

n

, pH and pL protonation and stepwise stability constants can be computed by different

[image:4.595.174.438.92.321.2]

Table 3: The pH titration reading of acid, acid + ligand (TRM - 1) and acid + ligand(TRM - 1) + metal ions.

Vol. of alkali added Acid Acid + ligand Acid + ligand + metal ions

Cu+2 Ni+2 Co+2

0.00 1.70 1.70 1.70 1.70 1.70

0.50 1.80 1.85 1.85 1.85 1.85

1.00 2.00 2.35 2.45 2.32 2.40

1.20 2.30 2.71 2.62 2.70 2.60

1.30 2.35 2.90 2.85 2.88 2.81

1.40 2.50 3.25 3.20 3.23 3.21

1.50 2.75 3.75 3.75 3.55 3.65

1.52 2.82 3.90 3.85 3.95 3.77

1.54 2.90 4.00 3.96 4.10 3.83

1.56 3.01 4.19 4.07 4.16 4.00

1.58 3.10 4.40 4.20 4.21 4.25

1.60 3.20 4.52 4.25 4.25 4.50

1.62 3.55 4.61 4.50 4.52 4.62

1.64 4.35 4.75 4.52 4.65 4.80

1.66 8.40 5.00 5.02 4.77 4.98

1.68 10.25 8.50 5.24 5.00 5.25

1.70 11.20 8.98 5.72 5.25 5.74

1.75 11.75 9.70 6.26 6.01 6.59

1.80 12.10 10.30 7.78 6.56 7.60

1.85 12.25 10.76 8.69 8.56 8.48

1.90 12.30 11.00 8.95

1.95 12.41 11.18 9.04 9.24 9.39

2.00 12.50 11.40 9.50

N° = 0.5, E° = 0.02 M, V° = 40.0 ml, TCL° = 5 × 10-3 M, TCM° = 1 × 10-3 M, t = 30 ± 0.2°C, u° = 0.1 M

Solvent = Dioxane : water 60 : 40 (v/v).

TITRATION CURVES OF (TRM-1) AND M(TRM-1)2

0 2 4 6 8 10 12 14

0 0.5 1 1.5 2 2.5

Volume of alkali added (ml)

p

H

m

et

er

r

ea

d

in

g

"

B

"

Acid Acid+Ligand A+L+Cu+2 A+L+Ni+2 A+L+Co+2

Figure 1: Graph of pH v/s volume of added NaOH of HNO3 acid, ligand(TRM-1) and Cu(II), Ni(II) and Co(II) ions

[image:4.595.110.502.349.603.2]

Table 4: 1-(3-bromo-4-hydroxy-5-methoxybenzylidene)thiosemicarbazide(TRM- 1) at 30°°°°±±±± 0.2°°°°C

B V1 – V2

n

_A

1

2

log

−

−

A A

n

n

_H

PK

₂

log

2.50 0.321 1.8042 -0.6135 3.1135

2.75 0.279 1.6967 -0.3613 3.1113

3.00 0.226 1.5640 -0.1118 3.1118

3.25 0.171 1.4252 0.1311 3.1188

3.50 0.116 1.2901 0.3887 3.1113

3.75 0.075 1.1876 0.6366 3.1134

4.00 0.046 1.1149 0.8865 3.1135

4.25 0.027 1.0680 1.1339 3.1161

4.50 0.016 1.0394 1.3877 3.1123

4.75 0.009 1.0226 1.6377 3.1152

5.00 0.005 1.0128 1.8845 3.1155

Average

log

PK

₂H = 3.1138

B V2 – V1

n

A

A A

n

n

−

1

log

H

PK

1

log

9.25 0.015 0.9626 1.4122 10.6612

9.50 0.026 0.9355 1.1613 10.6013

9.75 0.044 0.8908 0.9111 10.6611

10.00 0.072 0.8208 0.612 10.6612

10.25 0.112 0.7204 0.4114 10.6614 10.50 0.163 0.5920 0.1615 10.6615 10.75 0.221 0.4493 -0.0883 10.6617 11.00 0.275 0.3142 -0.3398 10.6610 11.25 0.318 0.2049 -0.5889 10.6611 11.50 0.350 0.1267 -0.8384 10.6616

Average

log

PK

₁H = 10.6613

FORMATION CURVE OF TRM-1 0

2

4

6

8

10

12

14

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

p

H

m

et

er

r

e

a

d

in

d

"

B

[image:5.595.199.413.93.394.2]

"

Figure 2: Graph of pH v/s

n

A [image:5.595.102.510.411.618.2]

LINEAR PLOT OF TRM-1

-2 -1.5 -1 -0.5 0 0.5 1 1.5 2

0 2 4 6 8 10 12 14

[image:6.595.89.536.68.310.2]

pH

Figure 3: Graph of pH v/s

1

2

log

−

−

A A

n

n

and

A A

n

n

[image:6.595.216.398.337.502.2]

−

1

log

Table 5: Copper + 1-(3-bromo-4-hydroxy-5-methoxybenzylidene)thiosemicarbazide(TRM- 1) at 30°°°°±±±± 0.2°°°°C

B V3 V2 V3-V2

n

pL

4.50 1.602 1.593 0.009 0.0958 11.7559 4.75 1.614 1.600 0.014 0.1749 11.0227 5.00 1.636 1.618 0.018 0.1957 10.2819 5.25 1.665 1.637 0.028 0.3183 9.5419 5.50 1.678 1.640 0.038 0.4745 8.8043 5.75 1.698 1.643 0.055 0.6868 8.0651 6.00 1.711 1.647 0.064 0.7992 7.3253 6.25 1.730 1.650 0.080 0.9985 6.5865 6.50 1.751 1.654 0.097 1.2107 5.8486 6.75 1.765 1.660 0.105 1.3106 5.1863 7.00 1.778 1.663 0.115 1.4352 4.7307 7.25 1.789 1.666 0.123 1.5351 3.6388 7.50 1.800 1.670 0.130 1.6225 2.8988 7.75 1.810 1.673 0.137 1.7096 2.1617 8.00 1.820 1.682 0.138 1.8145 1.8094 8.25 1.838 1.688 0.150 1.8832 0.4843

Table 6: Nickel + 1-(3-bromo-4-hydroxy-5- ethoxybenzylidene)thiosemicarbazide(TRM- 1) at 30°°°°±±±± 0.2°°°°C

B V3 V2 V3-V2

n

pL [image:6.595.216.397.531.681.2]

[image:7.595.100.511.88.571.2]

Table 7: Cobalt + 1-(3-bromo-4-hydroxy-5- ethoxybenzylidene)thiosemicarbazide(TRM- 1) at 30°°°°±±±± 0.2°°°°C

B V3 V2 V3-V2

n

pL

4.50 1.601 1.593 0.008 0.0903 12.0930 4.75 1.613 1.600 0.013 0.1499 11.3530 5.00 1.637 1.618 0.019 0.1968 10.6161 5.25 1.664 1.637 0.027 0.3205 9.8789 5.50 1.677 1.640 0.037 0.4623 9.1416 5.75 1.688 1.643 0.045 0.5744 8.4010 6.00 1.709 1.647 0.062 0.7866 7.6630 6.25 1.724 1.650 0.074 0.9989 6.9238 6.50 1.755 1.654 0.101 1.3081 6.1850 6.75 1.771 1.660 0.111 1.4105 5.4498 7.00 1.781 1.663 0.118 1.5110 4.7095 7.25 1.793 1.666 0.127 1.6226 3.9700 7.50 1.803 1.670 0.133 1.7096 3.2321 7.75 1.815 1.673 0.142 1.8090 2.4984 8.00 1.833 1.682 0.151 1.8828 1.7600

FORMATION CURVES OF M(TRM-1)

2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

0

2

4

6

8

10

12

14

pL

[image:7.595.218.397.92.251.2]

Copper(II)

Nickel(II)

Cobalt(II)

Figure 4: Graph of

n

v/s pL for Cu(II), Ni(II) and Co(II) ions

CONCLUSION

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